Design And Synthesis Of Bismuth-Based Photocatalvsts Materials With Abundant Oxygen Vacancies For Selective Organic Oxidation

In recent years,both environmental pollution and energy shortage have become more and more serious due to the rapid development of industry and the continuous growth of the population.Semiconductor photocatalytic technology can directly use solar energy to drive chemical reactions at room temperature,and it is widely used in environmental purification,production of clean energy,N₂ fixation,organic synthesis,etc.,which provides a promising sustainable strategy to solve the problems of environmental pollution and energy shortage.Bismuth-based semiconductor materials have attracted intensive attention in the field of photocatalysis owing to their unique electronic structures,suitable band gaps,and good stability.However,the shortcomings of single-semiconductor photocatalysts,such as the limited light absorption,poor carrier separation ability,and insufficient surface active sites,lead to unsatisfactory catalytic performance.In this dissertation,the bismuth-based semiconductors have been modified by a series of methods,such as constructing oxygen vacancies（OVs）,coupling OVs with noble metals,and constructing semiconductor heterostructures with modified surface,respectively.These modifications could enhance the ability of light absorption,promote the separation and transfer of photo-generated carriers,and improve the activation of reactant molecules,synchronously.Therefore the photocatalytic performance was significantly enhanced.The main research contents of this dissertation are described as follows:1.Bi₂Mo O₆ hollow microspheres were synthesized by solvothermal method and then calcined respectively in air and H₂/Ar atmosphere to adjust the concentration of OVs.The Bi₂Mo O₆-H₂-2h hollow microspheres obtained by calcining in H₂/Ar atmosphere for 2 h presented the enhanced visible light absorption,higher photocurrent response and charge transfer efficiency,due to the presence of abundant OVs,which effectively inhibited the electron-hole recombination and increased the carrier migration efficiency.In the photocatalytic selective oxidation of benzyl alcohol,Bi₂Mo O₆-H₂-2h hollow microspheres exhibited the superior performance for producing benzaldehyde and H₂O₂.In situ Electron paramagnetic resonance（EPR）detections demonstrated that the Bi₂Mo O₆-H₂-2h hollow microspheres are conducive to the generation of carbon-centered radicals and superoxide radicals,thereby boosting the selective oxidation of benzyl alcohol.2.The surface plasmon resonance（SPR）of Au nanocrystals can enhance the photocatalysis of semiconductors.Herein,Au-Bi₂WO₆ hybrid photocatalysts possessing a good combination of plasmonic Au nanoparticles（NPs）and abundant OVs were synthesized through a one-step solvothermal method.After the optimization of Au loading,the Au-Bi₂WO₆ hybrid photocatalyst with Au content of0.5wt%exhibited the outstanding activity and selectivity toward selective oxidation of aromatic amines under visible light（?>400 nm）,far outperforming pure Bi₂WO₆nanostructures with OVs.The collaborative contributions of hot charge carriers from Au NPs,photoexcited electron-hole pairs from Bi₂WO₆,and the OVs for efficient adsorption-activation of molecular O₂ resulted in the enhanced photocatalysis for selective oxidation under visible-light irradiation.This study highlighted the rational construction of metal-semiconductor hybrid photocatalysts with multiple active sites.3.The design and preparation of photocatalysts without noble metal are significant for reducing the cost of photocatalysts.Therefore,a novel photocatalyst consisting of OVs-rich Bi OCl nanoplates and bismuth-organic hybrid layer（Bi Cl₃Br-CTA）was synthesized by a one-step solvothermal process.The Bi Cl₃Br-CTA hybrid layer endowed the photocatalyst with broad visible light absorption and afforded super-oleophilic surface having a high affinity for toluene.Moreover,the Bi OCl/Bi Cl₃Br-CTA heterostructures facilitated the spatial separation of photogenerated charge carriers,and promoted the adsorption-activation of O₂ and toluene molecules.As a result,the Bi OCl/Bi Cl₃Br-CTA heterostructures photocatalyst exhibited excellent activity and selectivity for the C（sp³）-H bond oxidation of toluene,achieving benzaldehyde production rates of 3579 and 2416μmol·g^-1·h^-1 under full-spectrum and visible irradiations of simulated sunlight,respectively.The photocatalytic mechanism was revealed by the comparative experiments and in situ EPR detections.This research demonstrates an effective strategy to construct high-efficiency photocatalysts for the challenging organic transformations.